The broad objective of this project is to study the structural and functional aspects of tRNA recognition by aminoacyl-tRNA synthetase enzymes. The interaction of amino acid and ATP with yeast phenylalanyl-tRNA synthetase and yeast tyrosyl-tRNA synthetase will be studied kinetically and by equilibrium dialysis. The binding of tRNA to these enzymes will be studied under equilibrium conditions by gel-filtration chromatography. The alpha and beta subunits of yeast phenylalanyl-tRNA systhetase will be preparatively fractionated and the binding of all substrates to each subunit studied. The structural and functional aspects of several new tRNA species implicated in metabolic regulation will be studied in solution by optical and NMR methods. The effect of non-standard base pairs on the structure and stability of RNA hairpin helices will be studied.